Neacomys sp. B

Karyotype: 2n = 54 and FN = 66. Autosomal complement: seven metacentric and submetacentric pairs (five large and two small), and 19 acrocentric pairs medium to small decreasing in size. Sex chromosomes: X, a medium acrocentric; Y, a small subtelocentric. C-banding metaphases exhibited blocks of constitutive heterochromatin on the pericentromeric region of all autosomes. The X chromosome presented a pericentromeric heterochromatic block. The Y chromosome was almost entirely heterochromatic. G-banding was also performed. FISH with telomeric sequences revealed signals exclusively at the ends of all chromosome arms and no interstitial signals were observed (Silva et al. 2017, pp. 7, Fig. 3).

The authors established maps of chromosomal homology between the karyotype of Neacomys sp. A and Neacomys sp. B by using whole chromosome probes of H. megacephalus . The comparative genomic mapping between the two Neacomys species shows that these karyotypes differs by the occurrence of 11 fusion/fission events, one translocation, four pericentric inversions, and four heterochromatic amplification events (Silva et al. 2017).